Sankar Das Sarma

Hubert M. James Lecture Series 

October 6, 2011

Sankar Das Sarma is the Richard E. Prange Chair in Physics and a Distinguished University Professor at the University of Maryland. He is also a Fellow of the Joint Quantum Institute and the Director of the Condensed Matter Theory Center at Maryland. Das Sarma received his PhD from Brown University in 1979, and has been a faculty member at Maryland since 1980. His undergraduate degree is from Presidency College in Calcutta (Kolkata), India where he was born.

Das Sarma is an ISI Highly‐Cited Researcher having received more than 22,000 citations to his work in the literature. Das Sarma has mentored 25 PhD students and 85 postdoctoral fellows in his career. Das Sarma's research interests are the quantum theory of matter, statistical mechanics, and quantum information. His publications and expertise are broad, ranging over topics as disparate as topological quantum computation, fluctuations in financial markets, physics of high‐speed transistors, and exotic quantum properties of solids and atoms at ultra-low temperatures and in ultrahigh magnetic fields.

"Computing with Quantum Knots: Majorana Fermions, Non‐Abelian Anyons, and Topological Quantum Computation"

Abstract:
I will discuss the revolutionary new concept of topological quantum computation, which is fault‐tolerant at the hardware level with no need, in principle, of any quantum error correction protocols. Errors simply do not happen since the physical qubits and the computation steps are protected against decoherence by non‐local topological correlations in the underlying physical system. The key idea is non‐Abelian statistics of the quasiparticles (called 'anyons' as opposed to fermions or bosons), where the space‐time braiding of the anyons around each other, i.e. quantum 'knots', form topologically protected quantum gate operations.

I will describe in detail the status of the subject by discussing the theoretical principles guiding the experimental search for the appropriate topological phases of matter where such non‐Abelian anyons may exist. Among the most significant possibilities are certain even‐denominator fractional quantum Hall states, exotic chiral p‐wave superconductors, sandwich structures made from superconductors/semiconductors or superconductors/insulators, and suitably designed cold atomic systems.

In this context, I will also discuss the race to find Majorana fermions in solid state systems, with the Majorana fermions being the simplest generic examples of non‐Abelian objects in nature. I will explain how the subject of topological quantum computation synergistically brings together conformal field theory and advanced mathematics on one hand with materials science and quantum information on the other.